The present invention relates to an internal combustion engine having cylinder bank portions arranged in a V-shaped configuration and more specifically to an improved mechanism for driving the respective valve operating camshafts of each of the cylinder bank portions and to provide a more compact engine.
In V type engines and particularly those having pairs of overhead cam shafts for operating the valves of the cylinders of each bank, it is the practice to drive the cam shafts in timed relation to the engine crankshaft at one half crankshaft speed.
Some examples of the way this has been previously done are disclosed in Published Japanese Application 2003-286845(A). As described and illustrated therein, a valve operating camshaft of one of the bank portions is driven by a crankshaft drive gear via an endless timing drive belt. In turn and a second camshaft drive gear shaft is in meshing engagement with the crankshaft drive gear to be driven in a reverse direction. Through the drive of this gear shaft, a valve operating camshaft of the other bank portion is rotated in the direction opposite to the rotation direction of the valve operating camshaft of the one bank portion via another endless timing drive belt.
In addition, the tension applied to the endless timing drive belts of the respective bank portions is adjusted by hydraulic tensioners. Alternatively the hydraulic tensioners are both provided on the inner sides of the V-shaped bank portions or on the outer sides of the V-shaped bank portions.
As a result of this relationship and in order to drive the valve operating camshaft of one of the bank portions, the endless timing drive belt is directly wound around the crankshaft. Expansion or wear thus occurs in the endless timing drive belt due to the influence of variations in crank angle speed, which may cause a deterioration in reliability and durability.
In addition to the aforenoted problem, a speed reduction is required between the drive and driven ends to provide the correct valve timing. Further, due to requirements in terms of the durability, bending loss, and the like of the endless timing drive belt wound on the driven wheel side, there is a practical limitation to the reduction of the diameter of the driven wheel, which makes it difficult to achieve compact construction of the cylinder head.
In addition the offsetting of the axis of one of the camshaft driven wheels relative to the crankshaft axis tends to make the overall engine wider in a direction perpendicular to the crankshaft axis
It is, therefore, a principal object of the invention to provide a valve operating structure for an overhead cam V type engine that reduces the stresses on the crankshaft and timing mechanism and which also permits a compact engine construction.
It is a further object of the invention to provide an improved and compact V type engine construction wherein the transverse width of the engine may be reduced even if it employs twin overhead camshafts for each cylinder bank.